At present, ion mobility products, as an instrument for rapid detection of explosives and drugs, has been widely used in safety inspection fields in airport, subway and venue. Most of conventional ion mobility products use radioactive sources to generate reactive ions, but the radioactive sources has high risk and is strictly controlled, and thus cannot be used for safety inspection at places such as inside the aircraft. Accordingly, many companies began to do non-radioactive source product-based research since 90s of the last century. Currently, the market mainly focuses on several non-radioactive source technologies including corona discharge, photo-ionization source, electro-spray ionization source, glow discharge and the like, and, the corona discharge and photo-ionization source are main manners of ionization source adopted by most companies.
Reactive ions generated in the corona discharge are highly various in species and are closest to those generated in radioactive sources, so the corona discharge, among all these ionization sources, is the best choice as a substitute for the radioactive source. The corona discharge source has the disadvantages of fast loss and short in life, and thus is required to be frequently replaced, increasing degree of difficulty of the instrument design.
In the prior art, there is disclosed a needle-paired positive and negative pulse corona discharge source, and it has the advantages of being able to generate both positive and negative ions, and control the reaction process between sample molecules and reactive ions by controlling a time interval between an ion gate opening signal and a pulse corona. The use of pulse effectively prolongs the needle's life, but it is still inevitable that a tip of the needle will loss. Its disadvantage is that the needle has a short life and thus needs to be replaced periodically.
There is also disclosed a direct current switching corona source. When it is switched to high voltage, reactive ions generated at a corona metal wire can make the doped molecules to be charged, while when it is switched to low voltage, the reactive ions cannot make the doped molecules to be charged. The purpose of using this is to achieve a controllable doped condition. Photo-ionization has a simple principle and is easy to realize, but its disadvantage is that the life is short. The higher the corona voltage is, the faster the needle tip losses. The more active the background gas is, the more serious pollution of the needle is.
Although frequency of usage of the high voltage is reduced by adopting the voltage switching method (i.e., a corona high-voltage is switched on to perform a corona discharge when operated while the corona high-voltage is switched to a lower level so that no corona discharge will be performed when not operated), the life of the corona source is still low.